Think about that for a moment, and let it set in. If that is indeed the case, if the 42-year-old is unable to come back, or unwilling to go through the grueling rehab required to pitch again, then this is truly a sad day for baseball.

Rivera was injured on Thursday in Kansas City while shagging balls during batting practice, his knee buckling as he crumpled awkwardly to the dirt of the warning track. He was diagnosed with a torn ACL, prompting Yankees manager Joe Girardi to say “this is bad. There’s no question about it.”

A gifted athlete, Rivera has been shagging balls his whole career. As Keith Olbermann relays in his blog, Joe Torre once said Rivera was easily his best defensive center fielder.

“Yes, he’s a great outfielder,” Torre said, “He’s always bugging me to let him play there in a game. But does anybody really think I’d be crazy enough to let him play in a game? What if he got hurt?”

How prescient, and how unfortunate.

This is not how legends are supposed to go out. Our final image of Rivera in uniform should not be of him writhing on the warning track, or being carried to the cart by his teammates. It should be of him tipping his hat to the crowd as he walks off the mound after saving one last victory.

A career ERA+ (which measures his ERA against his peers, with 100 being average) of 206.

And then don’t forget the postseason: 42 saves in 96 games. A 0.70 ERA and a 0.759 WHIP. And five championship rings.

But even though the numbers are amazing and worthy of Cooperstown enshrinement on their face, they are only part of the Mariano Rivera picture.

Throughout his career, from setting up John Wetteland on the 1996 championship team, to pitching these past 18 years in the fishbowl atmosphere of the Bronx, Rivera has carried himself with a level of class and grace rarely seen in life, let alone in sports. The greatest closer of all time might also be the most universally respected athlete in sports. When he does decide to retire, whether tomorrow or sometime down the line, he will hang up his cleats as the last player – fittingly — to wear No. 42, which was retired across baseball in 1997 to honor the great Jackie Robinson.

It’s too early to know how long Rivera will be out, and if he’ll come back. Chipper Jones missed nearly eight months with a similar injury in 2010-11. Rivera was non-committal as he fought back tears and talked to reporters after Thursday’s game.

“At this point, I don’t know,” Rivera said. “At this point, I don’t know. Going to have to face this first. It all depends on how the rehab is going to happen, and from there, we’ll see.”

Here’s hoping the injury is not as bad as feared. Here’s hoping that even if it is, Rivera decides to come back, even if only for one more trip to the mound. He might not care for the burden of a season-long farewell tour. It’s simply not his style. But this is no way for a legend to go out.

Mariano Rivera deserves a better sendoff.

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